1. Field of the Invention The present invention relates to an induction heating furnace for melting metals through induction heating and a bottom tapping mechanism thereof
2. Description of the Related Art
In the case of producing a high purity metal or a metal alloy of desired components by melting a high reactive metal, attention has focused on an induction heating furnace which is capable of ensuring an uniform temperature over the entirety of a molten metal by induction heating and agitation to prevent variations in quality, and also suppressing the mixing of impurities into the molten metal to a low level, to prevent reduction in quality.
A conventional induction heating furnace has a side wall extending so obliquely as to increase an aperture from a bottom having a tapping portion to a certain point and then rising up vertically therefrom to an upper edge with the aperture kept at a constant diameter, as disclosed by, for example, Japanese Laid-open Patent No. Hei 4(1992)-327342. The side wall is formed by a plurality of longitudinally split, conductive segments arrayed circumferentially and insulated from each other. At the outer periphery of the side wall, an induction coil is arranged so that a metal at the inside of the side wall can be heated by induction heating. The tapping portion is provided with a mold to which a tapping passageway is communicated vertically. With the induction heating furnace thus constructed, the metal is melted by induction heating and then the molten metal flows into the tapping passageway of the mold, so as to be taken out with being solidified.
Also, Japanese Laid-open Patent No. Hei 8(1996) -145571 discloses an induction heating furnace including a side wall rising up vertically from a flat bottom having a tapping portion to an upper end, with an aperture kept at a constant diameter; and a bottom lid for closing the tapping portion. This induction heating furnace is so designed that when metal is melted by induction heating, the bottom lid can be melted to open the tapping portion, so as to take out the molten metal.
With the former arrangement in which the mold is provided at the tapping portion, a solidified layer in the tapping passageway in the mold and a solidified layer on the side wall become connected with each other. Due to this, taking out the metal from the mold requires a very large drawing force, thus causing difficulties in taking it out. Also, with the latter arrangement in which the tapping portion is closed with the bottom lid, once the bottom lid is melted to open the tapping portion, the tapping portion cannot be closed until all molten metal has completely been taken out. Due to this, switching between the melting of the metal and taking out the molten metal cannot be made smoothly. In short, the conventional type arrangements have a first problem that the melting of the metal and the task of taking out the molten metal cannot be made with ease and the switching operation between the melting of metal and taking out the molten metal cannot be made smoothly.
Further, where the side wall rises up with the aperture kept at a constant diameter, as in the above-described arrangement, when metallic vapor evaporates from the molten metal surface or the components of the gas produced in the molten metal dissipates from the molten metal surface, the evaporating direction of the metallic vapor or the rising direction of the gas become parallel to a wall surface of the side wall. Thus, the conventional arrangements have the second problem that the metal easily adheres to the side wall, thus requiring labor in the cleaning of the side wall, while the gas readily contacts the side wall to increase the flow resistance of the exhaust gas, which hinders the gas from being fully eliminated and causes a reduction of quality.
Accordingly, it is an object of the present invention to provide an induction heating furnace capable of solving at least one of the first and second problems described above, and a bottom tapping mechanism thereof.
According to a feature of the present invention, the above and other objects are accomplished by a novel induction heating furnace which comprises an accommodating vessel having a bottom, a tapping portion formed at the bottom, and a side wall formed by a plurality of longitudinally split, conductive segments arrayed circumferentially and insulated from each other for accommodating a to-be-melted material therein while cooling it; a coil arranged at an outer periphery of the tapping portion and the side wall for subjecting the to-be-melted material in the accommodating vessel to induction heating; a power source for supplying power to the coil; and a power source control for controlling the power source so that the tapping portion can be selectively switched between open and closed states by the melting and solidification of the to-be-melted material.
This construction can provide the following results. When the to-be-melted material accommodated in the accommodating vessel is subjected to induction heating, the to-be-melted material is melted while the molten material at the part contacting the side wall and a bottom wall of the accommodating vessel and the wall surface of the tapping portion is cooled and solidified. Thus, the power source control controlling the induction heating by the power source enables the tapping portion to be closed by the solidified material when the to-be-melted material is melted, and to be opened by melting the solidified material when the melted material is taken out. This enables the melting and removal of the material to be facilitated and also enables the switching operation between melting and takeout to be made with ease.
The induction heating furnace according to the invention may comprise an accommodating vessel having a bottom, a top edge portion and a side wall extending so obliquely as to increase in radius from the bottom to the top edge portion and formed by a plurality of longitudinally split, conductive segments arrayed circumferentially and insulated from each other; a coil arranged at an outer periphery of the side wall for subjecting a to-be-melted material accommodated in the accommodating vessel to induction heating; and a power source for supplying AC power to the coil.
This construction can provide the following results. When AC power is supplied to the coil from the power source, an alternating magnetic field is generated by the coil, whereby the to-be-melted material accommodated in the accommodating vessel is subjected to induction heating and is melted. When the to-be-melted material is thus melted material, the to-be-melted material evaporates at the molten material surface, and also components of gas produced in the molten material are discharged therefrom. At that time, the rise of the evaporated material and of the vaporized gas is not obstructed by the side wall, because the side wall of the accommodating vessel extends so obliquely as to increase in radius from the bottom to the top edge portion. Thus, almost no evaporated material contacts the side wall above the molten material surface, so that the drawbacks caused by the to-be-melted material adhering to the side wall are reduced. In addition, since almost no gas contacts the side wall, the flow resistance of the exhaust gas can be reduced and the gas can be fully eliminated.
Also, the induction heating furnace according to the present invention may comprise an accommodating vessel having a bottom, a top edge portion, a tapping portion formed at the bottom, and a side wall extending so obliquely as to increase in radius from the bottom to the top edge portion and formed by a plurality of longitudinally split, conductive segments arrayed circumferentially and insulated from each other; a coil arranged at an outer periphery of the tapping portion and the side wall for subjecting a to-be-heated material in the accommodating vessel to induction heating; a power source for supplying AC power to the coil; and a power source control for controlling the power source so that the tapping portion can be selectively switched between open and closed states by melting and solidification of the to-be-melted material.
This construction can provide the following results. When AC power is supplied to the coil means from the power source, an alternating magnetic field is generated by the coil, whereby the to-be-melted material accommodated in the accommodating vessel is subjected to induction heating and melted. When the to-be-melted material is so melted, the to-be-melted material evaporates from the molten material surface, and components of gas produced in the molten material are discharged therefrom. At that time, the rise of the evaporated material and of the vaporized gas is not obstructed by the side wall of the accommodating vessel because the side wall extends so obliquely as to increase in radius from the bottom to the top edge portion. Thus, almost no evaporated material contacts the side wall above the molten material surface, so that the drawbacks caused by the to-be-melted material adhering to the side wall are reduced. In addition, since almost no gas produced from the molten material contacts the side wall, the flow resistance of the exhaust gas can be reduced, and so the gas in the molten material can be fully eliminated.
Further, the control of induction heating by the power source can provide the result that when the to-be-melted material is to be melted, the tapping portion is closed by the solidified material, while when the melted material is to be taken out, the tapping portion is opened by melting the to-be-melted material. This enables the melting of the to-be-melted material and the takeout operation to be facilitated and also enables the switching between the melting and the takeout operations to be made with ease.
The tapping portion of the above-described induction heating furnace has an inlet portion which is joined to the bottom of the accommodating vessel and is so formed that an aperture of the inlet portion is gradually reduced in diameter from a top toward a bottom; and a hollow cylinder-like outlet portion is integrally formed with the inlet portion and is located below the inlet portion.
This construction can provide the result that the solidification of the to-be-melted material progresses along the wall surface of the tapping portion and then runs into the inner periphery. Accordingly, the closing operation of the tapping portion starts from the bottom of the inlet portion having a smallest aperture and progresses in sequence toward the top. Due to this, the entirety of the tapping portion can be prevented from being abruptly closed by a great force caused by solidification of the to-be-melted material, which allows the opening degree of the tapping portion to be varied with ease. As a result, the molten material can be taken out while the tapping amount of the molten material is finely adjusted.
Also, the coil of the induction heating furnace has an integral form comprising a first coil portion arranged at an outer periphery of the side wall and a second coil portion arranged at an outer periphery of the tapping portion, and the power source control controls the power source so that when the material is to be melted, the tapping portion is closed by part of the solidified material, whereas when the molten material is to be taken out, the part of the solidified material is allowed to melt to open the tapping portion.
This construction can provide the result that the first and second coil portions can be continuously formed by a single coil.
Also, in the induction heating furnace, the coil may be separated into a first coil portion arranged at the outer periphery of the side wall and the second coil portion arranged at the outer periphery of the tapping portion; the power source may comprise a first power source for supplying power to the first coil portion and a second power source for supplying power to the second coil portion; and the power source control may control the first power source and the second power source independently.
This construction can provide the result that the melting of the material and the takeout of the molten material can be done independently to provide improved productivity.
Preferably, the second power source comprises a melt-use power source portion for producing a first frequency of AC power to the extent that the to-be-melted material can be allowed to melt; and a solidification-use power source portion for producing a second frequency of AC power to the extent that the to-be-melted material is allowed to solidify, and the power source control functions such that when the tapping portion is opened, AC power can be produced from the melt-use power source portion, whereas when the tapping portion is closed, AC power is produced from the solidification-use power source portion.
This construction can provide the result that the tapping portion can be easily switched between open and closed states by switching between the melt-use power source portion and the solidification-use power source portion, and the tapping amounts can be easily adjusted by adjusting the time for supplying the high frequency power and the low frequency power.
Desirably, the induction heating furnace according to the invention may further comprise a drawing portion for forcibly drawing the to-be-melted material out from the tapping portion. This construction can provide the result that even when solidification of the melt is in progress, the to-be-melted material can be forcibly drawn out from the tapping portion, to obtain the to-be-melted material in a desired solidification state.
The induction heating furnace enables the to-be-melted material to be melted under a reduced pressure. This construction enables a proper use under a reduced pressure in which a large amount of gas is produced.
Also, a bottom tapping mechanism of an induction heating furnace includes: an inverted hollow-cone-shaped aperture bored in a bottom of an accommodating vessel for accommodating therein a molten material of a to-be-melted material; a funnel-shaped tapping portion comprising an inlet portion formed inside the aperture while contacting an inner periphery thereof and a hollow-pipe-like outlet portion integrally formed with and located below the inlet portion, the tapping portion being divided into a plurality of segments by a plurality of slits which are continuous to each other and are connected to cooling water feed/discharge pipes; induction heating coils arranged around the tapping portion at the inlet portion and the outlet portion, respectively; and a solidification-use power source portion and a melt-use power source portion which are selectively connected to the induction heating coils arbitrarily. This construction can provide the result that the time for the melt and the tapping of the molten material and the amount of the molten material can be controlled with a relatively simple structure.
Preferably, the above-described tapping portion comprises an inlet portion which is wide at a top end thereof and gradually narrows toward a bottom end thereof; and a hollow-pipe-like outlet portion extending downward in continuation to the inlet portion. This construction enables the opening degree of the tapping portion to be varied with ease, so that the molten material may be taken out while the tapping amount of the molten material is finely adjusted.
Further, the bottom tapping mechanism of the induction heating furnace is so constructed that when the tapping of the molten material is done, high-frequency power is supplied to the induction heating coils arranged around the tapping portion at the inlet portion and at the outlet portion, respectively, whereas when the tapping of the molten material is stopped, low frequency power is supplied thereto. This construction enables the bottom tapping mechanism to have a further simplified construction.